Three-dimensional image displays have been used for years. These displays typically employ spherical lenses (integral displays) or cylindrical lenses (lenticular displays). Both the integral and lenticular displays typically use a single plastic sheet incorporating an array of convex spherical or cylindrical lens surfaces that are molded, embossed, compressed, or cut into the surface of the plastic sheet. These designs typically employ narrow lenses with a small focal length to control aberrations and increase image quality. A portion of the image to be displayed, hereinafter referred to as a sub-image, is placed at or near the focal surface of each lens. The sub-image width is typically equal to or less than the center to center spacing or pitch of the individual lenses of the array. Accordingly, the narrow lens limits the amount of information or number of picture elements which can be present in each sub-image. The field angle over which the three-dimensional image is viewed is limited by the lens pitch and with most previous designs by the lens width. Increasing the width of the lenses so that the sub-image width can be concurrently enlarged increases the numerical aperture of the lenses, resulting in increased aberrations over the entire field of view, particularly at large field angles.
To obtain the best quality image throughout the viewing angle, the sub-images should be placed along the best image surface of each lens. However, the image surface of the lenses is typically a small-radius curve; it has proven difficult to produce a similarly curved sub-image. Accordingly, three-dimensional displays employ a flat image substrate that lies only partially in the image surface of each lens, resulting in a three-dimensional image which degrades for increasing field angles. U.S. Pat. No. 3,503,315 describes forming-spherical sub-image surfaces in photographic films which record and display a three-dimensional image as a complex means of solving this problem.
The apparent depth of a three-dimensional image is directly proportional to the number of resolvable picture elements in each sub-image. Because the focal length of the individual lenses is typically small, the number of resolvable picture elements, and therefore the apparent depth of the images, is limited. Since the displays are typically small and are perceived at close viewing distances, such limited apparent depth does not substantially degrade display performance. However, when viewed at an increased distance, the limited apparent depth degrades the overall three-dimensional effect of the display.
Another problem is that each sub-image must be aligned with a corresponding lens of the lens array to within approximately one picture element in order to create the desired overall three-dimensional image quality. The photographic film which typically carries the sub-images is somewhat dimensionally unstable, particularly in comparison to the material making up the lens array. In order to maintain alignment, it is necessary to either increase the size of the picture elements, thereby decreasing apparent depth of the image, or to limit the overall size of the display so that the proper alignment can be achieved and maintained over all lenses in the array. This is another factor limiting the size of three-dimensional displays. In attempts to compensate for this phenomenon, practitioners have placed the photographic emulsion directly upon the back of the lens arrays to allow the emulsion and lens arrays to shrink or expand together. This solution, however, requires specialized equipment and processing, which greatly increases the cost of the resulting product.